The present invention relates to an improved double lumen catheter wherein an expandable or inflatable balloon element can be longitudinally stretched into a reduced cross section to permit easy pre-inflation positioning within blood vessels.
Various catheter devices including a balloon catheter have been developed for dilating occluded blood vessels, for example. The balloon catheter includes a balloon element which, during positioning, is kept in a non-inflated condition to permit easy emplacement relative to an occlusion. When the balloon element is disposed immediately adjacent the occlusion being treated, it is expanded or inflated by introducing pressurized fluid into the balloon element to dilate the occlusion. It is preferable that the balloon element in its non-inflated condition have a small outer diameter so as to enable easy insertion or movement within blood vessels. However, there is the conflicting requirement that the balloon element have a large outer diameter so as to have an increased cross section when inflated, so that dilatation can be achieved more effectively and efficiently. Japanese Laid-Open Patent Application No. 53-125386 offers an effective solution to this problem by providing a double lumen catheter which comprises an elongated flexible outer tube, an elongated flexible inner tube disposed in and extending through the outer type for relative movement to each other and a balloon element fixedly attached at its respective ends to the distal ends of the outer and inner tubes. In inserting the balloon catheter into a blood vessel, the outer and inner tubes are relatively displaced in opposite directions so as to stretch the balloon element longitudinally to have a reduced cross section.
However, the catheter of the aforementioned type has the disadvantage that due to the flexible nature of the outer and inner tubes which are generally made of an elastic material, it is not possible to stretch the balloon element sufficiently to obtain a reduced cross section as desired.
Accordingly, it is a primary object of the invention to provide an improved balloon catheter assembly wherein the balloon element can be stretched lengthwise to its full extent by preventing the stretching of the catheter tubes which would otherwise reduce the tension in the balloon.